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 ~ Licensed to the Apache Software Foundation (ASF) under one
 ~ or more contributor license agreements.  See the NOTICE file
 ~ distributed with this work for additional information
 ~ regarding copyright ownership.  The ASF licenses this file
 ~ to you under the Apache License, Version 2.0 (the
 ~ "License"); you may not use this file except in compliance
 ~ with the License.  You may obtain a copy of the License at
 ~
 ~   http://www.apache.org/licenses/LICENSE-2.0
 ~
 ~ Unless required by applicable law or agreed to in writing,
 ~ software distributed under the License is distributed on an
 ~ "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 ~ KIND, either express or implied.  See the License for the
 ~ specific language governing permissions and limitations
 ~ under the License.
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
package org.apache.sling.cli.impl.pgp;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import org.apache.commons.io.IOUtils;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.sling.cli.impl.ComponentContextHelper;
import org.apache.sling.cli.impl.http.HttpClientFactory;
import org.bouncycastle.bcpg.ArmoredInputStream;
import org.bouncycastle.openpgp.PGPException;
import org.bouncycastle.openpgp.PGPObjectFactory;
import org.bouncycastle.openpgp.PGPPublicKey;
import org.bouncycastle.openpgp.PGPPublicKeyRing;
import org.bouncycastle.openpgp.PGPPublicKeyRingCollection;
import org.bouncycastle.openpgp.PGPSignature;
import org.bouncycastle.openpgp.PGPSignatureList;
import org.bouncycastle.openpgp.PGPUtil;
import org.bouncycastle.openpgp.operator.bc.BcKeyFingerprintCalculator;
import org.bouncycastle.openpgp.operator.bc.BcPGPContentVerifierBuilderProvider;
import org.bouncycastle.openpgp.operator.jcajce.JcaKeyFingerprintCalculator;
import org.jetbrains.annotations.NotNull;
import org.osgi.service.component.ComponentContext;
import org.osgi.service.component.annotations.Activate;
import org.osgi.service.component.annotations.Component;
import org.osgi.service.component.annotations.Reference;

@Component(service = PGPSignatureValidator.class)
public class PGPSignatureValidator {

    @Reference
    private HttpClientFactory httpClientFactory;

    private static final String KEYS_FILE = "/tmp/sling-keys.asc";
    private PGPPublicKeyRingCollection keyRingCollection;

    public ValidationResult verify(Path artifact, Path signature) {
        try (InputStream fileStream = Files.newInputStream(artifact);
                InputStream signatureStream = Files.newInputStream(signature)) {
            InputStream sigInputStream = PGPUtil.getDecoderStream(signatureStream);
            PGPObjectFactory pgpObjectFactory = new PGPObjectFactory(sigInputStream, new BcKeyFingerprintCalculator());
            PGPSignatureList sigList = (PGPSignatureList) pgpObjectFactory.nextObject();
            PGPSignature pgpSignature = sigList.get(0);
            PGPPublicKey key = keyRingCollection.getPublicKey(pgpSignature.getKeyID());
            if (key == null) {
                throw new IllegalStateException(String
                        .format("Signature %s was not generated with any of the known keys.", signature.getFileName()));
            }
            pgpSignature.init(new BcPGPContentVerifierBuilderProvider(), key);
            byte[] buff = new byte[1024];
            int read;
            while ((read = fileStream.read(buff)) != -1) {
                pgpSignature.update(buff, 0, read);
            }
            return new ValidationResult(pgpSignature.verify(), key);
        } catch (PGPException | IOException e) {
            throw new IllegalStateException(String.format("Unable to verify signature %s.", signature.getFileName()),
                    e);
        }
    }

    @Activate
    private void readKeyRing(ComponentContext componentContext) {
        ComponentContextHelper helper = ComponentContextHelper.wrap(componentContext);
        String keysFile = helper.getProperty("sling.keys", KEYS_FILE);
        Path keysFilePath = Paths.get(keysFile);
        if (Files.notExists(keysFilePath)) {
            try {
                try (CloseableHttpClient client = httpClientFactory.newClient()) {
                    HttpGet get = new HttpGet("https://people.apache.org/keys/group/sling.asc");
                    try (CloseableHttpResponse response = client.execute(get)) {
                        try (InputStream content = response.getEntity().getContent()) {
                            IOUtils.copy(content, new FileOutputStream(keysFilePath.toFile()));
                        }
                    }
                }
            } catch (IOException e) {
                throw new IllegalStateException(
                        "Cannot download Sling key file from https://people.apache.org/keys/group/sling.asc", e);
            }
        }
        try (InputStream in = Files.newInputStream(keysFilePath)) {
            InputStream bouncyIn = org.bouncycastle.openpgp.PGPUtil.getDecoderStream(in);
            if (bouncyIn instanceof ArmoredInputStream) {
                ArmoredInputStream as = (ArmoredInputStream) bouncyIn;
                List<PGPPublicKeyRing> keyRings = new ArrayList<>();
                while (!as.isEndOfStream()) {
                    PGPPublicKeyRingCollection collection = new PGPPublicKeyRingCollection(as,
                            new JcaKeyFingerprintCalculator());
                    Iterator<PGPPublicKeyRing> readKeyRings = collection.getKeyRings();
                    while (readKeyRings.hasNext()) {
                        PGPPublicKeyRing keyRing = readKeyRings.next();
                        keyRings.add(keyRing);
                    }
                }
                if (!keyRings.isEmpty()) {
                    keyRingCollection = new PGPPublicKeyRingCollection(keyRings);
                } else {
                    throw new IllegalStateException(String.format("Sling keys file from %s does not contain any keys.", keysFile));
                }
            }
        } catch (IOException | PGPException e) {
            throw new IllegalStateException(String.format("Cannot read Sling keys file at %s.", keysFile), e);
        }
    }

    public static class ValidationResult {

        private boolean valid;
        private PGPPublicKey key;

        ValidationResult(boolean valid, @NotNull PGPPublicKey key) {
            this.key = key;
            this.valid = valid;
        }

        public boolean isValid() {
            return valid;
        }

        @NotNull
        public PGPPublicKey getKey() {
            return key;
        }
    }
}